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基于酸化剥离蛭石的TiO2光催化剂的负载与可控合成研究
王兰
学位类型博士
导师王传义
2012-05-27
学位授予单位中国科学院研究生院
学位授予地点北京
学位专业材料物理与化学
关键词蛭石 负载 Tio2 {001}晶面 绿色合成
摘要TiO2作为一种环境友好光催化材料,在光催化降解有机污染物、光分解水制氢、太阳能电池等领域具有卓越表现,并在解决环境污染和能源危机方面被寄予厚望。制备易于分离和回收且具有优良光催化性能的负载型TiO2光催化剂,有利于TiO2光催化氧化技术在污水处理中的工业化应用。同时,发展简单、绿色方法可控合成具有特定晶面的锐钛矿型TiO2纳米晶,对于研究其晶面与性能的关系并最终实现TiO2光催化剂的更广泛应用具有重要意义。基于此,本论文在蛭石的改性、基于酸化剥离蛭石进行的TiO2光催化剂的负载与可控合成方面进行了系统的探索研究。 以经过钠化处理的新疆蛭石为原料,分别采用热液搅拌法和机械球磨法获得了层间距为5.01 nm和5.24 nm的大层间距有机蛭石(OVMTs),其可用于纳米复合材料研究和环境污染物治理领域;同时,采用无机酸改性方式获得具有大比表面积、表面富含反应性基团、高热稳定性的酸化剥离蛭石(DVMT),并将其用于表面、界面作用研究。 基于DVMT片层的优良结构特性,以盐酸为钛醇盐的水解抑制剂,采用原位水热法制备了DVMT表层负载平展海绵状的三元混合晶相TiO2薄层复合光催化剂,发现该光催化剂具有比未经负载的TiO2更高的光催化活性;经过研究DVMT含量对该负载型光催化剂结构和性能的影响,得到了最佳的Ti与DVMT比例(Ti/DVMT比)为25 mmol/g;在此基础上,以硝酸作为抑制剂得到了与盐酸体系相似的催化剂结构组成和负载模式,同样具有较好的光催化性能;而在硫酸体系中得到的产物是一种DVMT表层负载平展的TiO2层并在该层之上生长了单层纳米TiO2颗粒球的锐钛矿型复合光催化剂,其光催化活性相对较低。此类易于分离和回收利用的负载型TiO2光催化剂的获得为改善TiO2光催化剂的固载工艺提供了新的思路。 以Ti/DVMT和酸物种为基础,研究了制备体系中pH值对负载型光催化剂结构和性能的影响,发现随着pH值的增大,产物中TiO2的晶相从三元混合相向单一锐钛矿相转变,并伴随着比表面积的增加和结晶度的降低,在pH = 0.5条件下获得的光催化剂的活性最高。在此基础上,进一步研究了煅烧温度对负载型光催化剂的影响,筛选出最优煅烧条件为500 °C,并发现负载型光催化剂中DVMT层的存在能很好地抑制TiO2晶型的转变,这为TiO2光催化剂的更广泛应用提供了有力证据。 鉴于材料晶体结构各向异性取向生长特性,以DVMT协同有机碱为形态控制剂,水热合成了{001}和{100}晶面主导的锐钛矿型TiO2长方体纳米单晶, 并通过调节DVMT与TTIP的比例,获得了不同形貌和晶体结构的锐钛矿型TiO2纳米晶,充分发挥DVMT片层的形态控制效应和二维片层的“硬模板”作用,有效稳定了{001}高能面并抑制锐钛矿型TiO2纳米晶在c轴方向上的生长。这种简单的绿色合成方法为其它功能型氧化物的合成提供了重要的思路和借鉴。
其他摘要Titanium dioxide (TiO2), one of eco-friendly catalytic materials, has very important applications in photocatalytic degradation of organic contaminants, photocatalytic splitting of water, solar cells, etc., holding great promise in solving the environmental pollution and energy crisis. Preparing of supported TiO2 photocatalyst being separable and recyclable easily and with good photocatalytic activity will help the industrialized application of photocatalytic oxidation technology in wastewater treatment. In addition, developing facile and green methods towards controllable synthesis of TiO2 nanocrystals with large percentages of high-energy facets is highly desired for the wide applications of TiO2 semiconductor materials. In this dissertation, systematic explorations have been carried out on the modification of vermiculite (VMT), as well as the controllable synthesis and immobilization of TiO2 photocatalysts based on acid-delaminated vermiculite. Using the Na+-exchanged vermiculite (Na-VMT) prepared from the VMT in Xinjiang area as the material, organo-vermiculites (OVMTs) with basal spacings of 5.01 nm and 5.24 nm were successfully prepared by a hot solution and a novel ball milling methods, respectively, and they are expected to be useful in the fields of nanocomposites and environment pollution treatment. Furthermore, acid-delaminated VMT (DVMT) was obtained by an inorganic acid-treatment method, which gives rise to large specific surface area, abundant reactive groups on the surface, and high thermal stability. The DVMT will be employed in surface and interface regulations or modifications. Through an in-situ hydrothermal route with hydrochloric acid as a hydrolysis inhibitor of titanium alkoxide, DVMT-supporte were prepared, which exhibited higher photocatalytic activity than the TiO2 obtained under the same conditions. And the optimum Ti/DVMT ratio of 25 mmol/g was determined by correlating the Ti/DVMT ratio with the structure and properties. Moreover, the HCl and HNO3 acidic media are in favor of the formation of a tri-phase and flat spongy-like thin layer of TiO2 accompanied by large specific surface areas, thus leading to excellent photocatalytic activity. Meanwhile, the composites obtained in the presence of H2SO4only has anatase TiO2 with ball-like aggregates on a thin layer with relatively small specific surface area, giving rise to relatively low photocatalytic activity. In addition, the preparation of DVMT-supported TiO2 composites with superiority in separation and recovery from the water treatment system provides a new approach for the immobilization technology of catalystsd TiO2 photocatalysts with flat spongy-like aggregates covering the DVMT layers completely to form a ternary mixed crystal phases TiO2 layer Following the optimization of the Ti/DVMT ratio and acid, the influence of pH in the preparation system on structure and properties of the DVMT-supported TiO2 photocatalysts was further explored. It was found that, the ternary mixed crystal phases of TiO2 were transformed to single anatase phases, accompanied by the increase in specific surface area and lowering crystallinity with increasing pH. Moreover, the transition temperature of anatase-rutile for the DVMT-supported TiO2 photocatalysts obtained at the optimum pH of 0.5 was significantly increased in the presence of DVMT, and the photocatalysts treated at 500 °C gives the highest photocatalytic activity. These are beneficial for the DVMT-supported TiO2 photocatalysts to be used more widely. Well-defined anatase TiO2 nanocuboidswith dominantly exposed {001} and {100} facets was synthesized via a hydrothermal route using DVMT and organic base as synergistic morphology-controlling reagents. Systematic investigations suggest that the DVMT layers act as effective hard template selectively stabilizing the {001} facets of anatase TiO2 and effectively retarding the crystal growth along c-axis. The reported green method may be adaptable to other metal oxides that are of strong catalysis or photocatalysis interest.
文献类型学位论文
条目标识符http://ir.xjipc.cas.cn/handle/365002/4364
专题环境科学与技术研究室
作者单位中国科学院新疆理化技术研究所
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王兰. 基于酸化剥离蛭石的TiO2光催化剂的负载与可控合成研究[D]. 北京. 中国科学院研究生院,2012.
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